Our research program is devoted to studies concerned with biochemical mechanisms involved in circadian phenomena, ranging from the ultimate molecular "clock," whatever it may be, to the factors involved in the expression of rhythms - the overt "hands of the clock." Our laboratory activities will be devoted to the following problems: (a) Activity Rhythms of Enzymes in Human Red Blood Cell Suspensions: Rhythms in isolated red cells implicate a mechanism not involving a nucleus. Membranes are suggested. (b) Membrane Mobility Agents: Compounds which alter the fluidity of membranes might alter the period of the clock if membranes are involved. (c) Overt Rhythmicity: Measurement: Equations elaborating a model of the overt rhythms may be useful in understanding how the "hands" of the "clock" are controlled. (d) Overt Rhythmicity: Biochemical Mechanisms: Changes in enzymes or proteins may be the biochemical basis for rhythmic alterations. (e) Chemical Agents (Inhibitors): Agents which alter the phase and/or period of rhythmicity are being studied. (f) Mixing: Is There Communication Between Cells?: Experiments are designed to detect possible effects of cells in one phase upon cells in another. BIBLIOGRAPHIC REFERENCES: Schmitter, R.E., Njus, D., Sulzman, F.M. Gooch, V.D., and Hastings, J.W. Dinoflagellate bioluminescence: A comparative study of in vitro components. J. Cell. Physiol. 87, 123-134 (1976). Hastings, J.W., Aschoff, J.W.L., Bunning, E., Edmunds, L.N., Hoffman, K., Pittendrigh, C.S., and Winfree, A.T. In The Molecular Basis of Circadian Rhythms (J.W. Hastings and H.-G. Schweiger, eds.), pp. 49-62, Group Report l: Basic Features, Abakon Verlagsgesellschaft, Berlin, Germany (1976).